There is known, as a conventional art, a resin composition such as a photo-sensitive resin composition and a curing type aqueous resin composition in which a polycarbodiimide compound is used as a curing agent (see, for example, PTL1 and PTL2). A polycarbodiimide compound is excellent as a curing agent of a resin composition, because of having low toxicity. Polycarbodiimide, however, has the problems of being low in solubility in various solvents, and also being difficult to store for a long period even in a cold dark place because the state of a solution thereof causes a reaction of a carbodiimide group and aggregation of a polymer to gradually progress, thereby forming gel.
In order to solve such problems, there is known, as a conventional art, a modified polycarbodiimide compound that has very excellent storage stability due to modification of polycarbodiimide derived from an aromatic diisocyanate compound with diisopropylamine (see, for example, PTL3).